Electrostatic printer



May 19, 1959 c. J. YOUNG 2,887,023

ELECTROSTATIC PRINTER Filed Nov. 26, 1951 5 Sheets-Sheet 1 lNVENTOR f/qzfffzawy May 19, 1959 Filed Nov. 26, 1951 C. J. YOUNG ELECTROSTATIC PRINTER 5 Sheets-Sheet 2 "ff lf il l W Ul We W 1* w `|1| M l il l Mi 1M INVENTOR May 19, 1959 c. J. YOUNG ELECTROSTATIC PRINTER 5 Sheets-Sheet 3 Filed Nov. 26, 1951 May 19, 1959 c. J. YOUNG 2,887,023

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United States Patent O ELECTRGSTATIC PRINTER Charles I. Young, Princeton, NJ., assignor to Radio Corporation of America, a corporation of Delaware Application November 26, 1951, Serial No. 258,219

Claims. (Cl. 95-1.7)

The present invention relates to an electrostatic printer or printers employing electrophotography, and, more particularly, although not necessarily exclusively, to a novel electrostatic printer capable of operating continuously and automatically to produce prints by electrophotography or the action of an electrostatic charge which is modified by impingement of light energy.

In accordance with the invention, in its broader aspects, a moving endless charge receiving surface, which may be a photoconductive surface, for example, is continuously exposed to electrostatic charging means. A light image, of letter type, for example, is produced and projected on the endless charged surface either intermittently, for example a line of type at a time, or continuously by the production of successive elementary image strips. The moving surface, following exposure to the light image, however it may be applied, is subjected to a continuously maintained and preferably transverse ow of developer mix. The nature of the developer mix will be more fully described hereinafter for the sake of completeness of disclosure, although it is not part of the present invention. The ow of developer mix develops a latent image for transfer to the surface of a web or sheet. The charged moving surface bearing the developed or powder image, a succession of such images, or successive parts of one such image is contacted in the presence of a member or members providing an electric charge by a web or sheet, of treated or untreated paper, or the like which receives the charge. Close interfacial contact between the charge receiving surface and the web or sheet is insured by the charge at the former surface. The contact lbetween the web and the charge receiving surface need be maintained over a relatively short linear distance of the latter. The light sensitive charge receiving surface is next 'subjected to a cleaning operation thereby to remove any remaining developer. It is to be understood that the invention may be practiced by having a stationary endless charge receiving surface along or around which charging instrumentalities, a web contacting device and a cleaning means are moved.

In the illustrative embodiment of the invention, disclosed herein, the endless charge receiving surface is provided on a cylinder, and preferably on the interior of a cylindrical member. The initial charge imparted to the charge receiving surface by relative movement between the charge receiving surface and a charging device is or may be closely followed by application of the light image or elements of the latter. This arrangement of means used in producing the print permits the recorder to be used in a subdued light. The quantity or bulk of the developer mix may be maintained below an excessive value to avoid loss of the latent image in a recorder embodying the present invention. Also, the rate of flow of developer mix may be controlled within suitable limits.

In the illustrative embodiment of the printer of this invention, the charging devices and cleaning means may be mounted in desired and changeable positions around the cylinder.

ICC

The principal object of the present invention is to provide a printer for printing continuously on a sheet or web by electrophotographic or electrostatic printing methods. Unattended automatic operation of printers constructed to embody principles of operation disclosed herein is also contemplated by this invention.

Another object of the invention is to provide a printer for printing by electrophotographic or electrostatic printing methods employing an endless charge receiving surface in the nature of a photoconductive surface for example. :7

A further object of the invention is to provide a printer for printing by electrophotographic or electrostatic printer methods employing a cylinder having a charge receiving surface thereon and preferably on the exposed interior surface of the cylinder.

A still further object of the invention is to provide a printer for printing by electron photographic or electrostatic printing methods having novel means for supporting and moving an endless sheet or web.

A still further object of the invention is to provide a novel arrangement of charging devices and means for applying a developer mix to a charge receiving surface in a printer for printing by electron photographic or electrostatic printing methods.

A still further object of the invention is to provide a novel arrangement for directing a luminous image, formed by a cathode ray tube, for example, onto the charge receiving surface of an electrophotographic or electrostatic printer.

Other objects and advantages of the invention will, of

course, become apparent and immediately suggest themselves to those skilled in the art to which the invention is directed from a reading of the following specification in connection with the accompanying drawings in which:

Fig. l is a view in top plan showing, diagrammatically, a printer embodying the present invention associated with a cathode ray tube for producing a radiant energy or luminous image of subject matter to be recorded on a sheet or web of recording material;

Fig. 2 is a view in side elevation of the apparatus shown diagrammatically in Fig. l;

Fig. 3 is a view in elevation of the printer of Figs. l and 2 as seen from the right-hand side;

Fig. 4 is a section, the section being taken on line 4--4 of Fig. 3 as viewed in the direction of the arrows;

Fig. 5 is a section, the section being taken on line 5-5 of Fig. 3 as viewed in the direction of the arrows; and

Fig. 6 is a vertical section, the section being taken on line 6 6 of Fig. 4 as viewed in the direction of the arrows.

Referring to the drawing, and for the present, to Figs. l and 2 thereof, reference character 10 designates the illustrative embodiment of the printer of this invention in its entirety. The printer 10 includes mechanical driving means, the principal part of which -is the shaft 12. Driving power is imparted to the shaft 12 from a motor 14 through pulleys 16 and 18 and a belt 19. The motor 14 may be of variable speed type or the belt and pulley arrangement may be replaced or preceded in the driving system by a suitable variable speed gear drive (not shown). The motor 14 should be capable of maintaing any selected operating speed reasonably constant.

The printer 10 has a fixing means such, for example, as the electrical or other type of heater 22 associated with it. The heater 22 may be included -in the structure off the printer. The printer 10 also includes a suitably supported recording web driving and guiding mechanism indicated generally by reference character 24.

As will appear hereinafter, the light sensitive photoconductive surface of the printer 10 is so arranged that a luminous image may be projected thereon in a direction initially extending parallel to the axis ofthe printer. The light sensitive surface is cylindrical and, in the illustrative example, is presented by the interior surface 25 of a cylindrical member 27 (Fig. 5). In the arrangement of Figs. 1 and 2, the luminous image to be recorded is produced by a cathode ray tube 26 which is mounted in a suitable protective shielding housing 28. A lens system 31 serves to project the image appearing on the face of the cathode ray tube onto the light sensitive surface of the receiver. The printer 10, including the web driving and guiding means 24, is mounted on a base 33. This base provides a convenient support also for the housing 28 and the lens system 31. The base 33 is inclined to the horizontal when the printer is in use as indicated by the angle made by the base with a horizontal dashed line 34. The inclination of the base and hence the printer 10 provides a gravity induced ow of developer. The horizontal line 34 may represent a bench, table, or other support for the printer 10.

The cathode ray tube 26 is provided with the usual appliances as will be understood by those skilled in the art to provide deection of the cathode ray beam therein. This beam will be modulated by signals similar to video signals. Only horizontal deection means may be provided in which case the second coordinate of defiection will be provided by movement of the light sensitive or charge receiving surface 25 of the recorder. The cathode ray tube 26 may be operated so as to produce characters similar to typewritten characters arranged in a horizontal row with a plurality of characters being formed successively. The formation of the row of characters is cyclically repeated with the same or different characters produced. The arrangement for producing a scanning line or an image of any desired type on the face of the cathode ray tube is not part of the present invention and need not be further disclosed herein. An arrangement for successively producing type characters arranged in a row is shown in the copending application of Warren H. Bliss, Serial No. 213,389, filed March l, 1951, now Patent No. 2,762,862. As disclosed in that application, 32 letters, for example, may be traced successively in a horizontal row by deflection of the cathode ray beam in the tube 26. These 32 letters are or may be produced in 1740 of a second. The peripheral speed of the charge receiving surface of the recorder 10 is or may be such that its displacement is equivalent to the height of one line of type produced on the face of the cathode ray tube in 1A@ of a second. These figures are given by way of example only, and it will be understood that any luminous image, however produced, may be recorded by the recorder 10.

The recorder 10 comprises stationary end plates 38 and 39. The end plates 38 and 39 are united into a rigid structure and are spaced apart by a number of tie rods 42, for example three (Figs. 4 and 6). Screws 43 serve to clamp the end plates against ends of the rods 42. The end plates assembled with the rods 42 may rest upon or be secured to the base 33.

The end plates 38 and 39 are apertured and provided with bearings 46 (one of which appears in Fig. 3) in which the shaft 12 is journalled. A pair of rollers 48 (Fig. 2), each having a flange 49, receives the end plates 51 and 52 of the supporting arrangement for the cylindrical member 27. The end plates 38 and 39 are also apertured and provided with bearings 56 (one of which appears in Fig. 3) in which an idler shaft 58 is journalled. A pair of rollers 61 (one of which appears in Fig. 6), each having a flange 63 also receives the end plates 51 and 52. The rollers 48 in combination with the angularly displaced rollers 61 serve as a cradle upon which the cylindrical structure comprising the member 27 rotates.

The end plates 51 and 52 of the rotatable supporting structure for the cylindrical member 27 are joined by strips 70, 71, and 72 of sheet metal or the like. Each strip is turned upwardly at each end as indicated at 74. The ends 74 are engaged in radial grooves 76 in the plates 51 and 52 and are secured by screws 78. Each end plate has a circular groove 81 and a cylindrical member 83 formed of a transparent plastic sheet is engaged at its ends in the circular grooves. A circular sheet metal ring 86 is engaged in the groove 81 in the plate 51 to serve as a reinforcement for the cylindrical member 83. A similar metal ring 88 is engaged in the groove 81 in the end plate 52. The cylindrical member 83 is preferably, but not necessarily, made of transparent material for reasons later to be described in connection with operation of the machine while performing a recording operation.

The previously mentioned cylindrical member 27 is spaced from the circular member 83 by a plurality of helically arranged strips 89. In the illustrative example, fourteen strips 89 are provided. The strips 89 extend beyond the edge of the member 27 on the side of the rotatable device bounded by the end plate 51. This extension may be approximately one inch, for example. The ends of the strips 89 stop short of the edge of the cylindrical member 27 adjacent the end plate 52. For example, the strips may extend to within one-half inch of the edge of the cylindrical member 27. The strips 89 are disclosed and claimed in a copending application of Harold G. Greig, Serial No. 258,145, led November 26, 1951, now Patent No. 2,730,023. The function of the strips 89 will be fully described hereinafter for the sake of completeness of disclosure.

The cylindrical member 27 is a metal cylinder the inside surface 25 of which is polished and coated with a photoconductive material such as selenium for example. Aluminum is a suitable material. The selenium coating is applied by evaporation at reduced pressure. During the coating operation, the cylinder is mounted in a frame (not shown) so that it can be rotated slowly to expose the entire surface to the same concentration of selenium vapor. By way of example, during the coating process the cylinder can be rotated at a speed of slightly over 3 r.p.m. The selenium coating is in the neighborhood of 1/1000 of an inch in thickness.

The several appliances for obtaining the record on a paper Web as well as the web reel and the guide for the web are carried by the end plates 38 and 39 in such a Way that their position may be circumferentially adjusted about the interior of the photosensitive surface 25. The end plate 39 is recessed as indicated at 92 which is covered by a ring 94 to provide a circular groove 98. The ring 94 is secured to the end plate 39 by means of screws 96. The plate 38 is also recessed to provide a groove 95 in conjunction with a ring 99 similar to the ring 94. In the illustrative example of a printer involving the present invention, thecylindrical member 27 is rotatable in a counter-clockwise direction as viewed in Fig. 3 of the drawing.

The appliances associated with the photoconductive surface will be described in the order in which they cooperate with said surface beginning with the arrangement for cleaning the surface of excess developer mix or powder remaining following take olf on the paper Web of the characters to be recorded. Reference character 102 indicates a channel shaped member, the open side of which is spaced slightly from the photosensitive surface 25. The interior of this channel shaped member 102 is in communication with a conduit 103 which may be connected to any suction line or suction device such as, for example, a vacuum cleaner. The ends of the channel member 103 are effectively connected to at pieces or members 106 and 107 which are received in the grooves and 98 respectively.

The surface 25 is charged to a high positive potential in the illustrative machine 10 by a plurality of wires 108. These wires may, for example, be three in number and may be spaced 'M6 inch from the selenium surface. A bar member 112, provided with angularly turned ends 114 and 116 seated in the grooves 95 and 98, carries insulating wire holders 11S and 121 between which the wires 108 are stretched. The wires 108 are connected to a 6.5 kv.

source of positive potential, for example. A grid of Wires 124 are stretched between insulating wire holders 125 and 126. The latter are also secured to the bar member 112. In the illustrative example, nineteen wires 124 are provided which are spaced 1/s inch apart and grounded to the frame of the machine. The central portion of this grid of wires is 3/32 inch from the selenium surface. The dimensions are given solely by way of example.

As previously described, the image on the cathode ray tube 26 is projected on the selenium surface 25 by the lens system 31. This is accomplished by a mirror 131 which is inclined as shown with respect to the axis of the machine to project the image from the cathode ray tube face, or other image source, onto the surface 25 following exposure to the high positive potential applied by the wires 108. The image, so projected, is located axially along the surface 25. The mirror 131 is secured in any suitable manner to a metal or other sutliciently rigid strip 132. This strip is bent so as to provide radially extending ends 136 and 137 (Fig. 3) which are received'in the grooves 95 and 98, respectively.

A quantity of developer in the form of a powder, for example, is placed in the cylindrical member 27 and this powder flows axially along the surface 25. The path of powder flow is angularly displaced counter-clockwise from the line or lines of impingement of the image projected by the mirror 131 as viewed on Figs. 3 and 6 of the drawing. Suitable developers for xerography use are known and it will be understood that the machine 10 can be used with any suitable powder having predetermined ltribo-electric properties. A form of developer giving excellent results in the machine 10 is made up of glass beads and sulphur particles coated with coprecipitated organic coloring matter. The coloring matter is, for example, spirit soluble Nigrosine and spirit soluble Iosol Black. The glass beads are negative with respect to the sulphur coated with the coprecipitated coloring matter. The latter takes a positive charge. The `developer powder briey described herein as giving excellent printing results is fully disclosed in a copending application for Letters Patent of Harold G. Greig, Serial No. 187,827, iiled September 30, 1950, now Patent No. 2,727,826, and entitled Improvement in Electrostatic Printing.

In the illustrative machine 10, the quantity of developer is circulated by the helical strips 89 as the cylinder rotates. The developer powder may be circulated by other means such, for example, as an external pipe system, or a hopper may be provided from which the powder is fed onto the surface 25 at its elevated edge adjacent the end plate 39. The surplus developer after traversing the surface 25 may be collected in a second hopper after being discharged by gravity from the lower end of the cylinder.

The projecting ends of the strips opposite the end plate 38, as they continuously pass the lowest point of the rotating cylinder, scoop up or trap a quantity of the developer powder which rests by gravity in the lowermost part of the cylinder. It will be understood that as the cylinder rotates, the powder will ow at a controlled rate axially along the cylinder and that the path of ow will be displaced to the right of the axial plane of the cylinder as it is viewed in Figs. 3 and 6 of the drawing. This feature of a machine embodying the present invention provides some additional angular spacing between the wires 108 and the point of impingement of the luminous image on the surface 25. It will be understood that as the cylinder rotates the -developer which 'is trapped in the channels between the strips 89 will be discharged from these channels, and that the excess or overow, which is continuously transferred to the bottom of the cylinder, will flow across the cylindrical member. ,It will be noted that the strips 89 do not extend for the full length of the cylinder 27 to the right as viewed in Fig. 5. This permits smoother ow of the accumulated powder onto the inner selenium surface 25.

The paper web, designated by reference character 141,

is fed from a roll 143. This roll is conveniently mounted on a spindle 1'46 supported by brackets 148 and 149. A helical spring 151, bearing against a disc 152, assists in centering the roll by biasing it into contact with a second disc 153. The web 141, as it feeds from the roll 143, passes under a rod 161 so that it is substantially in contact with the surface 25. The rod 161 is carried by brackets 162 carried by an insulating member 163 which forms a part of a transfer unit for applying a negative charge over the exposed surface of the web 141. The web is held against the surface 25 by the electrostatic charge from the transfer unit and is peeled from the surface at the point where it passes over a second rod 166. The rod 166 is carried by a bracket 168 (Fig. 3) which is received in the groove 95. The other end of this rod is carried by a second bracket 169 (Fig. 4) received in the groove 98. A second rod 173 extends diagonally across the machine substantially in the horizontal plane of the rod 166. The rod 173 is supported at one end by the bracket 169 and at its other end by a bracket 176. 'Ihe bracket 176 is received in the groove 98. After passing over the rod 166, the paper web also passes over the rod 173 and passes from beneath this last named rod to an inclined rod 179 (Fig. l). The rod 179 forms part of the previously mentioned web driving and guiding means 24. The previously mentioned power shaft 12 drives a roll 182 through belt and pulley connections 183. The driven roll 182, along with an idler roll 186, forms a pair of driving pinch rollers through which the web is passed after being turned over the top of the inclined rod 179.

The transfer unit as shown in Figs. 3 and 4 comprises the previously mentioned insulating member 163 carried by brackets 188 and 189, received in the grooves 95 and 98. The member 163 is pierced at intervals to receive pointed electrodes such as needles 192 which project toward the portion of the web 141 in contact with the surface 25. A connection to each of the needles 192 from a suitable high voltage source (not shown) is made by a conductor 196. The outer ends of the needles are protected by a corona shield 197.

The overall operation of the machine will now be described. With the described appliances in position circumferentially of the machine, a roll of paper is mounted on the spindle 146 and is threaded beneath the rods 161 and 166 from which it passes over the angularly disposed rod 173. The paper, after being passed over the rod 173, returns beneath this rod to pass under the inclined rod 179 of the web driving and guiding mechanism 24. The web is drawn from the top of the rod 179 by the pinchrolls 182 and 186. Assuming that the motor 14 is operating and that luminous images are produced on the face of the cathode ray tube 26, the cylinder will rotate counter-clockwise as viewed in Fig. 3 of the drawing. The cylindrical member 83, if transparent, permits observation of circulation of the developer mix.

A high positive potential is applied to the wires 108 of the charging unit and the developing powder flows axially of the cylindrical surface 25. The illuminated portions of the selenium surface will be discharged and the developer powder will adhere to the portions which retain little or no charge. The cylindrical surface bearing the powder image is in contact with the moving web and transfer of the powder is effected by the negative charge applied by the needles 192. This mode of operation holds for the powder discussed above by way of example.

What is claimed is:

l. Recording apparatus for electrophotography comprising a cylinder having a photoconductivc interior surface, means to rotate said cylinder, electric charging means positioned to apply a charge to said surface, means progressively located in one direction with respect to said second named means for applying a light image to successively presented axial portions of said surface, means progressively located in said one direction with respect to said light image applying means for causing a gravity induced `ow of developer'material axially over said surface, means for supporting a vrecord receiving web on the interior of said cylinder whereby said web contacts said surface in an area thereof progressively spaced in said one direction from the region of developer material flow over saidsurface, and means for applying an electric charge affecting said record receiving web and said surface simultaneously at the location of contact between said record receiving medium and said surface.

2. Recording apparatus for electrophotography comprising a tubular member circular in cross section, a selenium coating on the interior surface of said member, said member having anged ends, a plurality of rotatable rollers providing a cradle upon which said hanged ends are seated, means to impart rotation to said tubular member, a plurality of wires in the interior of said tubular member positioned to apply a charge to said selenium coating, a source of high voltage connected to said plurality of wires, an angularly disposed mirror within said tubular member for reecting a light image from an image source exteriorly of said tubular member onto said surface at a location angularly spaced in one direction from said wires, means angularly spaced in said one direction from the location of application of the light image for causing a substantially continuous flow of developer material by gravity transversely over said surface, means within said tubular member for supporting a record receiving web supply, means to feed said web whereby said web contacts the selenium coating in an area thereof angularly spaced in said one direction from the region of developer material low, a plurality of needles for applying an electric charge affecting said record receiving web and said coating simultaneously at the location of contact between said record receiving medium and said coating, and a connection from a high voltage source to said plurality of needles.

3. Recording apparatus for electrophotography comprising a tubular member circular in cross section, a selenium coating on the interior surface of said member, means to impart rotation to said tubular member, a plurality of wires in the interior of said tubular member positioned to apply a charge to said selenium coating, a source of high voltage connected to said plurality of wires, an angularly disposed mirror within said tubular member for reflecting a light image from an image source exteriorly of said tubular member onto said surface at a location angularly spaced in one direction from said wires, means angularly spaced in said one direction from the location of application of the light image for causing a substantially continuous ow of developer material by gravity transversely over said surface, means within said tubular member for supporting a record receiving web supply, means to feed said web whereby said web contacts the selenium coating in an area thereof angularly spaced in said one direction from the regionof developer material ow, a plurality of needles for applying an electric charge affecting said record receiving web andsaid coating simultaneously at the location of contact between said record receiving medium and said coating, and a connection from a high voltage source to said plurality of needles.

4. Recording apparatus for electrophotography comprising a tubular member circular in cross section, a selenium coating on the interior surface of said member, said member having anged ends, a plurality of rotatable rollers providing a cradle upon which said llanges ends are seated, means to impart rotation to said tubular member, means in the interior of said tubular member positioned to apply a charge to said selenium coating, a source of high voltage connected to said means, an angularly disposed mirror within said tubular member for reilecting a light image from an image source exteriorly of said tubular member onto said surface at a location angularly spaced in one direction from said charge applying means, means angularly spaced in said one direction from the location of application of the light image for causing a substantially continuous ow of developer material by gravity transversely over said surface, a second means for applying an electric charge to said coating, following llow thereover of the developer material, and a connection from a high voltage source to said second charge applying means.

5. An electrophotographic recorder comprising a tubular member circular in cross section, said member having a photoconductive interior surface, means to support and rotate said member, means within said member for supporting a supply roll of a record receiving web, means for supporting the wex extending from said supply roll in contact with a portion of the interior of said tubular member, means to turn and guide the web in a direction axially of said tubular member, and means to impart movement to the web and thereby to remove the web from the supply roll.

References Cited in the le of this patent UNITED STATES PATENTS 607,648 Schwarz July 19, 1898 1,661,934 Fatscher et al Mar. 6, 1928 1,714,705 Wildhaber May 28, 1929 1,770,013 Rich July 8, 1930 1,840,289 Hunter Jan. 5, 1932 2,153,166 Wynd Apr. 4, 1939 2,357,809 Carlson Sept. 12, 1944 2,516,242 Munger July 25, 1950 2,551,582 Carlson May 8, 1951 2,573,881 Walkup et al. f Nov. 6, 1951 2,624,652 Carlson Jan. 6, 1953 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No., 2,887,023 May le, 195e Charles J. Young It is hereby certified that error appears in the -printed specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Signed and sealed this 16th day of February 1960.,

(SEAL) Attest:

KARL H. AXLINE ROBERT C. WATSON Attesting Officer Commissioner of Patents UNITED STATES PATENT OFFICE CERTIFICATE 0F CORRECTION Patent No, 2,887,023 May i9, 195e Charles J. Young It is hereb;r certified 'that error appears in the-printed specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Signed and sealed this 16th day of February 196C.,

(SEAL) Attest:

KARL H. XLINE Attesting Officer ROBERT C. WATSON Commissioner of Patents 

